The present invention relates to a polymerizable composition comprising first and second allyl functional monomers. More particularly, the present invention relates to a polymerizable composition of a first allyl functional monomer having at least two allyl groups that is selected such that a polymerizate of the first monomer has a 15 second Barcol 934 hardness of at least 40, and a second allyl functional monomer selected from polyether diol bis(allyl carbonate), polylactone diol bis(allyl carbonate) and mixtures thereof. The present invention also relates to polymerizates prepared from such polymerizable compositions, and photochromic articles prepared from such polymerizates.
Polymerizable organic compositions based on allyl functional monomers, such as polyol(allyl carbonate) monomers, e.g., ethylene glycol bis(allyl carbonate), and poly(allyl ester) monomers, e.g., diallyl isophthalate, and polymerizates obtained therefrom are well known in the art. Polymerizates of allyl functional monomers, such as polyol(allyl carbonate) monomers, possess excellent clarity, hardness and good flexibility, examples of which include, ophthalmic lenses, sunglasses, and automotive and aircraft transparencies.
Recently, photochromic plastic materials, particularly plastic materials for optical applications, have been the subject of considerable attention. In particular, photochromic ophthalmic plastic lenses have been investigated in part due to the weight advantage that they can offer relative to ophthalmic lenses made of inorganic glass. In addition, photochromic transparencies for vehicles, such as automobiles and airplanes, have been of interest because of the weight reduction and potential safety features that such transparencies offer. Photochromism is a phenomenon involving a change in color of a photochromic substance, or an article containing such a substance, upon exposure to light radiation containing ultraviolet rays, and a reversion to the original color when the influence of the ultraviolet radiation is discontinued. Examples of light sources that contain ultraviolet rays include sunlight and the light of a mercury lamp. Discontinuation of the ultraviolet radiation can be achieved, for example, by storing the photochromic substance or article in the dark, by removing the source of ultraviolet radiation or by filtering out the ultraviolet rays from the light source.
Fully cured polymerizates of many allyl functional monomers, e.g., polyol(allyl carbonate) monomers such as ethylene glycol bis(allyl carbonate), are not particularly well suited to the incorporation of organic photochromic substances by diffusion, e.g., by thermal transfer. In some instances, for example in the case of ethylene glycol bis(allyl carbonate), one or more organic photochromic substances may be incorporated by diffusion into an undercured polymerizate, followed by an additional curing step to fully cure the polymerizate having organic photochromic substances incorporated therein. Such two-stage cure processes require extra time and expense, and can result in inconsistent and unreliable incorporation of organic photochromic substances into the polymerizate.
It would be desirable to develop polymerizable compositions of allyl functional monomers that can be used to prepare substantially completely cured polymerizates into which organic photochromic substances may be incorporated. In addition, it would desirable that polymerizates prepared from such newly developed compositions have good physical properties, such as hardness and heat distortion temperature, and that photochromic articles prepared from such polymerizates have good photochromic properties, e.g., as measured by change in optical density (as described in further detail in the examples herein).
U.S. Pat. No. 4,742,133 describes the preparation of a poly(allyl carbonate) functional prepolymers by contacting a liquid monomer composition comprising at least one poly(allyl carbonate) functional monomer with oxygen. The poly(allyl carbonate) functional monomers of the ""133 patent are described as including those based on polyhydroxy functional chain extended compounds, such as ethylene oxide extended glycerol and compounds based on lactone extension.
U.S. Pat. No. 4,666,976 describes a polymerizable solution comprising polyol(allyl carbonate) monomer, liquid polyol(allyl carbonate) polymer or a mixture thereof, and bromoxylenol blue. The polyols of the polyol(allyl carbonate) monomer and liquid polyol(allyl carbonate) polymer are described in the ""976 patent as including polyol-functional chain extended compounds, e.g., ethylene oxide extended glycerol, and compounds based on lactone extension.
U.S. Pat. No. 5,973,093 describes polymerizable organic compositions of a first monomer component which is a polyol(allyl carbonate), and from about 2 to 35 weight percent of a second monomer component which is an alkoxylated bisphenol having acrylate or methacrylate functionality. Substantially completely cured polymerizates prepared from the polymerizable compositions of the ""093 patent are described as being used to prepare photochromic articles by incorporating a photochromic substance, e.g., by thermal transfer, into the polymerizate.
In accordance with the present invention there is provided a polymerizable composition comprising:
(a) a first allyl functional monomer having at least two allyl groups, said first allyl functional monomer being selected such that a substantially completely cured polymerizate of said first allyl functional monomer has a 15 second Barcol 934 hardness of at least 40 (as determined in accordance with American Standard Test Method No. D 2583-92 using a Model No. 934 Barcol Impressor); and
(b) a second allyl functional monomer, which is different from said first allyl functional monomer and is selected from,
(i) polyether diol bis(allyl carbonate);
(ii) polylactone diol bis(allyl carbonate); and
(iii) mixtures of (i) and (ii),
wherein said second allyl functional monomer (b) is present in said polymerizable composition in an amount to provide (ixe2x80x2) a substantially completely cured polymerizate of said composition having improved organic photochromic substance incorporation (as determined by measuring Net Absorbance at a wavelength of 390 nanometers, and as will be described further herein) relative to a substantially completely cured polymerizate of said composition free of (b), and (iixe2x80x2) heat distortion temperature of at least 40xc2x0 C. (as determined in accordance with American Standard Test Method No. D 648-86, at a deflection of 254 microns).